DAX: Rank measure needs tweaking

I just posted a question about running totals, but I have another about my rank measure. Here is what I posted earlier about my Data Model:

I am trying to model my data, which is approximately 7 million rows of product movement data. Included in the dataset are references to Shipment Date, Warehouse Number, Store Number, Product information (UPC), and the quantity of cases shipped.

I need help on multiple measures (I am reading Building Data Models with PowerPivot 2015 edition). For this problem I have a Matrix table showing Product description, Qty, Year Previous Qty, the % change between the two, a Product Ranking.

My Item Rank measure looks like this:

Qty Rank = IF ( HASONEVALUE( UniData[Desc] ) && [TotQty] > 0, RANKX ( ALLSELECTED( UniData[Desc] ), [TotQty] ), BLANK() )

This measure works great until the table is filtered to one item. Then of course the rank goes to 1. My intent is to rank the items within a Manufacturer (as a group). How can I change the measure to rank all items within a group (in this case as a manufacturer) regardless of whether they are being displayed or not?

Thank you!